feat: add expires_at field to request swap parameter encoding

[nmammeri]

Pull Request

Closes: PRO-1851

Checklist

Please conduct a thorough self-review before opening the PR.

• I am confident that the code works.
• I have written sufficient tests.
• I have written and tested required migrations.
• I have updated documentation where appropriate.

Summary

• Return estimated_expires_at field determining when the payload is considered expired.
• Only implemented for Bitcoin for now, Solana implementation should be straightforward when Solana vault swapping is in main
• Updated bouncer btc_vault_swap test to validate the expiry estimated_expires_at

[codecov]

Codecov Report

Attention: Patch coverage is 16.00000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 72%. Comparing base (8c4fd61) to head (0143d3c).

Files with missing lines	Patch %	Lines
state-chain/runtime/src/runtime_apis.rs	0%	11 Missing ⚠️
state-chain/runtime/src/lib.rs	29%	0 Missing and 10 partials ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #5506    +/-   ##
======================================
- Coverage     72%     72%    -0%     
======================================
  Files        495     495            
  Lines      88383   88282   -101     
  Branches   88383   88282   -101     
======================================
- Hits       63348   63174   -174     
- Misses     22467   22530    +63     
- Partials    2568    2578    +10     

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[kylezs]

See my comment on the linear issue, I think having an RPC endpoint will be much more robust and less error prone, and probably best not to have integrators depend on something we know will change.